A- 12 439 METAL CATALYZED OLIGOMERIZAT ON REACTIOINS-1 OF,ORGANOSILOXANES(U) MICHIGAN UNIV ANN ARBOR DEPT OFCHEMISTRY M D CURTIS 28 OCT 82 B S5 N00 4 78 C 0191

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Metal Catalyzed Oligomerization Reactions Tech. Report 1982of Organosiloxanes ______________

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Prepared for publication in J. Poy Sci. -Polymer Symposia.

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siloxanes

0.ABSTRACT IC.I0nu@ mi ," ouw ld- II n*.*04WV aid Idmiiyb 1m m

The metal catalyzed oligomerization of 1,3-dihydidodisiloxanesis reviewed. The formation of metallacyclodiuiloxanes of

LA1. (HMeRSi) 20 (RinPh, Benzyl, Me) and their role in the catalysis isdiscussed, as is the possibility of forming stersoregular silicones

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Technical Report No. S

Metal Catalyzed Oligomerization Reactions of

Organosiloxanes

by

M. David Curtis

Prepared for publication in

Journal of Polymer Science - Polymer Symposia Series

The University of MichiganDepartment of ChemistryAnn Arbor, MI 48109

October 28, 1982

Reproduction in whole or in part is permitted for any purposeof the United States Government.

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Ae-c-essi"oln For

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I

Metal-Catalyzed Oligomerization Reactions of Organosiloxanes

M. David Curtis, Department of Chemistry, The University

of Michigan, Ann Arbor, MI 48109

Abstract

Transition metal complexes, e.g. L 2Pt(C 2H4),

and L2 Ir(CO)Cl (L=PhP), react with tetraalkyldisiloxanes,

(HRR'Si) 2O, to produce metallacycles featuring the transi-

tion metal, two silicons, and the oxygen in a four-membered

ring, MSiOSi. When R=Me and R'=Ph, stereoselectivity in

the formation of the metallacycle from a mixture of stereo-

isomers of the starting disiloxane is observed. The

catalytic activity of these complexes for the oligomeriza-

tion of the disiloxanes has been investigated in the hope

of obtaining stereoregular silicones. It has been found

that extensive rearrangements occur which redistribute the

groups on the silicon atoms. Increased selectivity for the

desired exchange type (SiO-groups for Si-H) was found when

the catalysts were adsorbed on oxide supports. Although

the goal of synthesizing stereoregular silicones has not

yet been achieved, the results warrant further investigation.

(,

INTRODUCTION

Our research on the metal-catalyzed redistribution re-

actions of organodisiloxanes had its start several years ago

when two lines of research came together. The first of the

two lines was our interest in small ring metallacycles

which contained in the ring at least one transition element

and one or more of the heavier group IVa congeners, e.g.

Si or Ge. Small-ring metallacycles are of interest since

they have been implicated as intermediates in several transi-

tion metal-catalyzed reactions, e.g. olefin metathesis.1 3

Metallacycles are also probable intermediates in

several reactions of silacyclobutanes.4 For example, several

transition metal complexes catalyze the ring-opening poly-

merization of silacyclobutanes and disilacyclobutanes to

high molecular weight polycarbosilanes (eq. 1,2). 5

Me2Si + M .. [M -=-9(1 (--) (-SiMe,- (CH2 3- (i

ioM 2 -n ()

(()(

MeSi SiMe (cat.) (-SiMe2-CH2-) n

M2Si.1.Si 2 2-.--- 2S (2

Intermediate, 2, in eq. 1 may also be trapped with acetylenes

to form silacyclohexanes.1 0

The second line of research which merged into the pre-

sent work involved the use of polysiloxanes to anchor transi-

tion metal complexes for use as "supported homogeneous"

11catalysts. The most-used polymers for supporting transiti.-

2

metal complexes are modified, cross-linked polystyrene.

Usually, multi-step syntheses are required for the modifica-

tion and the degree of possible catalyst loading is limited

by diffusion problems. We reasoned that transition metal

complexes could be attached to polysiloxane polymers of the

type, [-Si(H)MeO-] n, due to the high reactivity of the Si-H

linkage toward low-valent metal complexes.

In fact, the Si-H bonds of the polymer [Si(H)MeOl n re-12

act with a variety of low-valent metal carbonyls, but the

resulting polymers were unstable, cross-linking and extrud-

ing metal complexes upon standing. In order to understand

such behavior, we turned to studying the reactions of

tetramethyldisiloxane, (HMe2Si) 20, since this disiloxane is

the simplest difunctional model characteristics of the re-

peating unit of the [-Si(H)MeO-] n polymer. It was found that

TMDS (tetramethyldisiloxane) reacts ruthenium and iron

carbonyls to give the five-membered metallacycles, 3.1 2

/S i-M(CO) 4M3(CO) 12 + (HMe2 Si)2 0 S (3)

Si-M(CO) 4(M = Fe, Ru)

The five-membered metallacycles are relatively inert and

possess negligible catalytic activity.

In contrast, complexes of Pd, Pt, and Ir were found to

give four-membered metallacycles, e.g. eq. 4-6 (L=Ph3P) .3

3

'/

L2 Pt(C2 H4 ) + (HMe2Si) 20 - L2 Pt 0 (4

( ) /I\2~ ~~ 2 2 2 Si.

L2 PdCl 2 + (HMe2Si)2 0 L Pd 0 (5)

( ,) I \

0

L2Ir(CO)C1 + (HMe 2 Si) 2 0 1 r 0 (6)2 2 L X I --, s iH

When excess TMDS was used in the synthesis of the metalla-

cycles, 4-6, a mixture of siloxane oligomers,

H(SiMe 20)nSiMe2H, was observed to form as a byproduct. It

was then established that these metallacycles acted as

catalysts (or catalyst precursors) for the disproportiona-

tion of TMDS as shown in eq. 7.

(n+l) (HMe2Si) 20 nMe2SiH2 + H(SiMe 2 0) nSiMe 2H (7)

(E'DnE')

We immediately recognized that eq. 7 is a unique re-

action in which a strong Si-O bond is cleaved in a neutral,

non-aqueous solution at room temperature.14 The reaction

(7) may be viewed as a metal-catalyzed exchange of R3SiO-

groups for H- on silicon (hereinafter denoted as a SiO/H

exchange), viz. eq. 8 (the exchanging groups are underlined).

Ei

4

HMe 2SiO'GiMe 2H + H SiMe2OSiMe2H H-SiMe 2H +

HMe2 SiO-SiMe2OSiMe2H (8)

It was postulated that the strain inherent in the four-

membered metallacycle weakened the Si-O bond and allowed its

facile cleavage into coordinated silylene and silanone

(eq. 9).13,14 Indeed, the crystal structure determination

of complex 6 showed the Si-O-Si angle to be 99..R, con-

siderably smaller than the usual 130-150 found in un-

strained siloxanes. The large Si-O-Si angle in siloxanes

has been attributed to the effects of (p-d)w bonding between

oxygen and silicon. Therefore, a decrease in the Si-O-Si

angle would imply loss of pn-d n bonding and consequent

weakening of the Si-O bond. In fact, the Si-O bond length

(1.68 A) in 6 is somewhat longer than Si-O bonds in un-0

strained siloxanes (1.63-1.65 A).

L2 (H)(CO)Ir S O L (H) (CO)Ir 0; L(H). (C)1 (9)

c~ Z) /\

A complex mechanism was proposed whereby the complexed

silanone (Me2Si=O) in 7 was then inserted into the Si-H bond

of the excess TMDS in solution. As the concentration of the

trimer (E'DE') increased, the Me 2Si=O could then insert into

its Si-H bond to give tetramer (E'D2E'), and so on (eq. 10).

7 7TMDS - HMe2SiOSiMe2 SiMe2MeH ) H(SiMe20) 3SiMe2H (10)

2iH -Me 2Si 2-M( E'DE') 2 2 (E'D2 E')

5

Reaction 7, the metal complex catalyzed oligomeriza-

tion of disiloxanes,potentially represented a new route to

polysiloxanes. The normal method of preparing polysiloxanes

involves the hydrolysis of dialkyldichlorosilanes (eq. 11)

to give linear polymer and cyclics (Dx , x=3,4). The cyclics

may be polymerized in turn to linear polymer by acid or

base catalysis (eq. 12). In these polymerizations, all the

SiOSi bonds are redistributed and loss of any possible

stereoregularity results.

HO(x+n)RR'SiCl2 - (RR'SiO)3 4 + (-SiRR'-O-)n (11)

H+

nDx H (-SiRR'-O-)nx (12)orBase

The metal complex-catalyzed polymerization of di-

siloxanes of the type, (HRR'Si) 20 (8), presents some

intriguing possibilities. Disiloxane, 8, would normally be

found as a mixture of three stereoisomers: a (d,£)-pair of

enantiomers (8a,b) and the meso-diasteriomer, 8c. These

isomers are shown with the R,S nomenclature below. If the

insertion of the metal into the Si-H bond proceeds with

R' R R R' R' R'# I I I I I

H-Si-O-Si-H H-Si-O-Si-H H-Si-O-Si-HU I , I I I IR R' R' R R R

8a(RR) 8b(SS) 8c(RS)

6

16retention of configuration at silicon, then two types

of metallacycle, 9a, b, would be formed from the mixture

of three isomers, 8a-c, e.g. shown in eq. 13. The RR or SS

R RR' ii

LnM +8a-c LnM Vi ' L +L 10 (13)+ ~ ~ S - +LnM--- S i0(3

R R'(2) (2b)

isomers would give only the transoid metallacycle, 9a, while

the RS isomer would give only the cisoid structure, 9b.

We reasoned that if these metallacycles were indeed

the catalytically active species in the oligomerization of

the disiloxanes, 8a-, then metallacycles 2 might lead

stereoselectively to syndiotactic polymer, Da, and the cis-

metallacycle, 9b, to isotactic 10b. Furthermore, if metalla-

R R R

h-O-Si(14)n , nRI R R

(aa) (lOb)

cycles 9a and 9b differ in energy by only -3 kcal/mole as

a result of 1,3-cross ring, steric interactions of the R,R'

groups, then the lower energy isomer would be formed with

a 100:1 preference over the higher energy isomer, leading

ultimately to the selective polymerization of only one of

the two forms 8a,b or 8c and giving essentially pure stereo-

regular silicone. It was with this objective in mind that

I*

7

we started our investigations into the metal complex-

catalyzed oligomerizations of disiloxanes.

EXPERIMENTAL METHODS

Analytical procedures. The oligomeric siloxane pro-

ducts were analyzed by GC and GC/MS methods. The analytical

column employed was a 14' x 1/8" S.S. column packed with

5% SE-30 on Chromosorb WHP (80-100 mesh) with He as the

carrier gas at a flow rate of 10 mL/min. Typical GC con-

ditions were: injector, 2500 C; detector, 3006C; tempera-

ture program, 2 min. at 400 C, then increase at 40C/min. to

225°C. Mass spectra were recorded on a Finnigan 4000

quadrupole spectrometer interfaced to the temperature pro-

grammable GC column and controlled by the INCOS data

acquisition system.

In those instances where MS alone could not differentiate

the products, e.g. between isomers, the products in question

were separated by preparative GC and analyzed by IH or 13C

NMR spectroscopy. Parent peaks were located by their mass

chromatograms (mass vs. time) or by using chemical ionization.

Once a compound's identity was definitely established, its

spectrum was stored in a computer library, and all future

occurrences of that compound in mixtures could be readily

ascertained by comparing its mass spectrum to that in the

library peak for peak.

8

Redistribution Reactions. The conditions for each run

are listed as footnotes in the Tables. A typical procedure

is described here. Tetramethyldisiloxane (42 mmole) was

added to 25 mL of a benzene solution containing 200 mg

(0.26 mmole) of L2Ir(CO)C1 under a N2 atmosphere. The re-

action flask was equipped with a reflux condenser, N2 inlet,

and gases were vented through an oil bubbler attached to the

top of the condenser. During the run, a static N2-blanket

was maintained over the reactants. After heating in an oil

bath for a given time, the solvent was stripped off under

vacuum (ambient temperature) and the residue and solvent

fractions analyzed as described above. During kinetic runs,

the reaction flask was also fitted with a small, septum-

tipped sidearm for periodic withdrawal of samples.

NOTATION

An abbreviated notation for siloxanes will be used

where appropriate. The siloxane is denoted according to

the functionality of the silicon and is based on the premise

that the "normal" organic substituent is the methyl group.

Thus, we use: E (end group) = Me3SiO11 2-, D (difunctional)

-O1/2 SiMe201/2-, T (trifunctional) = MeSiO 3 /2, Q = Si04/ 2.

A primed letter indicates H for Me substitution, i.e.

D' - HMeSiO2/ 2, E' = HMe2SiO1/2- , etc., and a superscript

"P" or "B" indicates P henyl or Benzyl substitution for

methyl, e.g. E P PhMe 2 SiO1 / 2 . Two superscripts indicates

9

a double substitution for methyl, e.g. E = HPdIeSiO1 /2.

Some examples of the use of this notation are given

below:

Me !.e

Me3 SiO-Si-O-Si-OSiMe 3 HPhMeSiOSiMe2OS iPhme 2

H H (EPDE )

(ED'D'E)

cyclo-(OSiMe2 )3 (Me3SiO) 3SiH (HBzMeSi) 20

(D3) (E3T') (E'BEB)

RESULTS AND DISCUSSION

Our initial premise that 1,3-cross ring interactions

might lead to stereoselective formation of one isomeric

metallacycle (e.g. 9a over 9b) from a mixture of stereo-

isomeric disiloxanes was quickly confirmed by the synthesis

17 1of the platinacycle, 11 (eq. 15, L = Ph3 P). The H-NMR

Me

CH2 Ph I

L 2 Pt-jI + (HMePhSi) 20 - L2 Pt (15)

CH2 Ph(11) Me

of 11 shows only one type of methyl group to be present,

so the isolated material must be either all cis or all

trans (11). The trans structure is favored on steric

grounds.

U

-.... -. .........EL~

10

In contrast, reaction of the benzyl methyl disiloxane,

(HMeBzSi) 2° (Bz = PhCH 2-), with L2Pt(C 2H4 ) gave a mixture

of the cis and trans metallacyles, 12a and 12b, in roughly

equal amounts as judged from the NMR spectrum. Apparently,

the benzyl group can swing around and lessen the 1,3 inter-

actions to the point that the energy difference between 12a

and 12b is minimal.

Bz MeCH 2 Bz z I

112e _i SiS i*2P- +(ezi)204L 24t-_ 2 P --- (6

2 (12a) Me (12b) MIeCH - Me Me

In a similar fashion, (HMeBzSi) 20 reacts with

L2Ir(CO)Cl to give a mixture of all three possible metalla-

cycles, 13a-c (R=Bz).17 Lack of stereoselectivity is also

observed when the octamethyltetrasiloxane, ED'D'E

(=[H(Me2SiO) (Me)Si-] 20) is allw.'w-d to react with L2Ir(CO)Cl.

Again, the spectral properties are consistant with the solid

being a mixture of the three metallacycles, 13a-c

(R=Me3SiO).18 The reaction of (HMePhSi)20 with L2 Ir(CO)CI

is even more complex and the nature of the products is not

definitely established.

0 0 Me MeR R

CCMe I~ C-i+L -_ _ I t - i- o L I. ' r -- i -- L -- -..1~ s _

H Me H R H Me R

- -Me e-------- - -q

The metallacycle, 11, and several other metallacycle

precursors were examined for their catalytic activity in

the redistribution or oligomerization reactions of

(HRMeSi)20 (R=Ph,Bz). If these disiloxanes were to react

in the same manner as TMDS (eq. 7), then the expected pro-

ducts would be as shown in eq. 17, 18. The actual products

(n+l)E' PE'P n PhMeSiH 2 + E'P(DP) nE'P (17)

(n+I)E' BE B - n BzMeSiH2 + E'B(DB)nE B (18)

observed for the reaction of (HPhMeSi) 20 (E'PE'P ) are shown

in col. 1 of Table I. Some monosilanes, e.g. Me3SiH and

PhMe2SiH, are found, but none of the expected PhMeSiH 2 is

present. However, some of the expected oligomeric products,

e.g. E' D E,2E (i.e. the lowest two members of the oligomers

shown in eq. 17), are indeed present. In addition to these

products, there is a variety of other products which appear

to be the result of redistributing the methyl, phenyl, and

hydrogen groups attached to silicon.

The formation of the monosilanes as indicated in Table

I suggested that reaction 17 does occur, but the initially

produced PhMeSiH 2 undergoes secondary rearrangement to give

the final products shown. Accordingly, PhMeSiH 2 was sub-

jected to metal-catalyzed redistribution conditions, and it

was observed that a rapid redistribution of all the groups

on silicon occurs to give the products shown in Table II.

For example, eq. 19 and 20 detail the formation of Ph 2MeSiHii2

12

and PhMe 2SiH, emphasizing the nature of the exchanges (Ph

for H and Me for H, or Ph/H and Me/H, respectively).

MeH 2Si-Ph + H-SiHMePh - MeSiH 3 + Ph2MeSiH (19)

PhH2Si---Me + H-SiHMePh - PhSiH3 + PhMe2 SiH (20)

These rearrangements of Si-C bonds are probably close

to being thermoneutral, so that the driving force is

essentially entropic, especially when a volatile substance,

e.g. MeSiH 3, Me2 SiH2 , etc., may be expelled from the re-

action. In fact, recent results show that the rate at which

volatiles are removed from the reaction can be rate limiting

and also effects the distribution of products. For the case

at hand, a mass balance for the products shown in column 2

of Table II reveals that the groups unaccounted for are in

the ratio, IMe:lSi:3H, i.e. MeSiH3 is the principal volatile3rproduct.

Column 3 of Table II shows that the rhodium catalyzed

disproportionation of PhMeSiH2 is very similar to the

iridium catalyzed reaction except that disilanes, e.g.

(HMePhSi-)2 , are also formed. This result is in accord

with that of Ojima et al.19 The formation of disilanes

seems to be a general result when rhodium or platinum based

catalysts are used.

We have observed that the rate of metal catalyzed dis-

proportionation of organosilanes is in the order,

• .. . '... .. . . .. . ... - ' 4 ... rir . .. I

13

RSiH 3 > R2 SiH 2 >> R3SiH >>> R4Si. Trialkylsilanes, R3SiH,

disproportionate only very slowly under our conditions,

The tetraalkylsilanes, R4Si, are essentially inert under the

mild conditions reported to date. Given this order of

activity, monoalkylsilanes, e.g. PhSiH3, which are the ex-

pected products of certain exchange reactions (Cf. eq. 20),

would undergo further, rapid exchanges and would not be

observed.

Returning our attention to the products shown in Table

I, the mono- and disilanes are ascribed to products from

the redistribution of groups on PhMeSiH 2 produced by the

reaction shown in eq. 17. The desired, oligomeric products,

, are formed in SiO/H exchanges as shown in eq. 21n

for the first member of the series (n=l). The remaining

HPhMeSi--OSiMePhH + H-SiMePhOSiMePhH -

PhMeSiH 2 + HPhMeSi--OSiMePh---OSiMePhH (21)(EPDPE P )

disiloxanes, e.g. E'PEP (= HPhMeSiO-SiMe2Ph), are formed as

a result of Me/H, Ph/H, and Ph/Me exchanges on the starting

disiloxane, E'PE'P , and on the oligomeric siloxane products.

The benzylmethyl disiloxane. EIBElB. was also subjected

to the redistribution reaction and results similar to those

found for E'PE'P were observed. The lower boiling mono-

silane fractions were composed of redistribution products

of BzMeSi1 2, e.g. BzMe 2SiH (36"), Bz2MeSiH '30%), and

* I

14

disilanes, e.g. (HBzMeSi-)2 (11%) were found.

At this point, it appeared very likely that the "metalla-

cycle" mechanism,13 if operative at all, was not the sole

mechanism for redistributing the organic groups on siloxanes

since the dialkylsilanes, R2SiH2, undergo a very rapid ex-

change. In order to further confirm this, several other

substrates were subjected to redistribution catalysis.

Pentamethyldisiloxane, Me3SiOSiMe2H(EEI), should be incapable

of readily forming a four-membered metallacycle since the

second silicon lacks a reactive Si-H functionality. However,

this disiloxane does undergo a slow redistribution in the

presence L2Ir(CO)C1 (2 mole %) at 700C to give predominately

ED'E, as well as lesser amounts of other Si3, and Si4 7

polysiloxanes (eq. 22). 18 A rather surprising facet of this

EE' ) ED'E + EDE + EDE' + EDD'E + E'D2E' +.. (22)2

(60%) (5%) (6%) (6%) (6%)

redistribution is that the ED'E is the result of a SiO/Me

exchange (eq. 23) which is an unexpected result since Si-H

bonds are much more reactive toward low-valent metal com-

plexes than Si-C or Si-O bonds. Thus, a SiO/Me exchange is

the result of compounding two "improbable" bond cleavages.

2Me 3SiOSiMe2H -* Me 3SiOSi(H)MeOSiMe 3 + Me 3SiH (23)

(EE') (ED'E)

All of the redistribution reactions of disiloxanes

initially exhibit a rapid, brief drop in disiloxane

iI

15

concentration, followed by a slow zero-order rate of con-

sumption. From the zero-order portion, a turn-over number

of 1.1 x 10- 3 moles EE'/(mole Ir)/min. may be obtained.

This is only 16 times slower than the observed turn-over

number for TMDS (E'E') under comparable conditions. 18 This

modest difference in rates again indicates that a special

metallacycle mechanism is not the primary mechanism for the

redistribution.

The trisiloxane, E'DE', also undergoes a slow redis-

tribution in the presence of L2 Ir(CO)Cl at 706C to give the

products shown in eq. 24. The cyclic product, D3D', may

E'DE' - EID 2 E' + D 3 D' + E'D 3E' + E'D +... (24)

(38%) (48%) (6%) (5%)

arise from the "internal" SiO/H exchange on EIDD'DE' (an

expected product from E'D/Me exchange on E'DE') as shown in

eq. 25.

i I

Me2Si - H SiMe2H: Me Si - 0

(Osi) 1, Me 2SiH 2 + (OSi) (25)

(O\ n In

These results forced a re-examination of our working

hypothesis. What kind of mechanism could be invoked to

explain these results? Especially disturbing was the

preponderance of SiO/Me exchanges which are difficult to

rationalize on the basis of known silyl-transition metal

chemistry.

4

16

Classifying the observed products according to their

exchange type reveals that in the L2Ir(CO)CI-catalyzed re-

distribution of TMDS (E'E'), 86% of the exchanges are

SiO/H and 24% are SiO/Me. With L3RhCI as catalyst, only

50% of the products come from SiO/H exchanges.

It is known that low-valent metal complexes rapidly

insert into Si-H bonds, but will insert into Si-C or Si-O

bonds only very slowly in most circumstances. (In fact,

a preferential insertion into a Si-C or Si-O bond over Si-H

has-never been observed.) The mechanistic question then

reduces to the question of how the Si-C and Si-O bonds are

activated when attached to a silicon bearing an Si-H bond

(keeping in mind that the rate of R2SiH 2 exchanges is much

faster than the rate of R3SiH exchanges).

In order to account for the Si-C and Si-O bond activa-

tion, we proposed that dinuclear complexes, e.g. 14, are

produced in the reaction mixture, and that these dinuclear

complexes are responsible for the observed SiO/Me, R/R',

etc. exchanges (eq. 26).20

R RR' R Si . L l J R' RjRSL

* Ln-M M-L M M__1 H/ SiR2R1 S i -I I /'_ "2 HLn SiR3

n R ~(26)

(14)

If dinulcear complexes are indeed the catalytically

active species in the exchangc eadctions, then immobilizing

_ _ _ _ _ _ __ _ _ __ _ _ __ _ _ _ __ _ _ _ _

17

the metal centers on solid supports should inhibit SiO/Me

exchanges, but possibly allow the SiO/H exchanges to pro-

ceed through mononuclear species. This hypothesis was tested

by adsorbing the catalyst precursors on a variety of in-

organic supports, e.g. alumina , silica, or alumina-silica.

Indeed, the reactions of E'E' (eq. 7) proceeded much faster

and gave higher selectivity for the desired SiO/H exchange

(see Fig. 1). The most dramatic increase in selectivity

occurred with 1% L3RhC1 on y-alumina (followed by heating

the catalyst to 700 for 4 hr. in vacuo). This catalyst

gave a SiO/H exchange selectivity of 99%, compared to the

50% selectivity of L3RhCl as a homogeneous catalyst. In

no case was the desired selectivity less than about 93% at

catalyst loadings of 1% or less. Higher catalyst loadings

gave lower selectivities, a result consistent with dinuclear

(adjacent) metal centers causing SiO/Me exchange, and mono-

nuclear centers giving SiO/H exchange.21

SUMMARY

Certain transition metal complexes of Pt, Rh, and Ir

have been found to be catalyst precursors for a redistribu-

tion reaction of siloxanes which leads to polysiloxanes.

Analysis of the oligomeric products reveals that the pre-

dominant redistribution is one which exchanges groups a-

to the Si-H functionality and that these groups exchange

predominately with the Si-H gz(oup. High selectivity for

' '~

18

SiO/H exchange is achieved with complexes supported on in-

organic oxides, e.g. SiO 2, A1203 , etc.

Further work in progress includes the extension of the

heterogeneously catalyzed reaction to disiloxanes of the

type, (HRMeSi)20 (R=Ph, CF3CH2CH 2-, etc.) with the aim of

establishing the stereochemistry of the resulting oligomers.

Should the reaction prove to be stereoselective, conditions

will be sought which would lead to high molecular weight,

stereoregular silicones. Such polymers may exhibit interest-

ing properties, e.g. piezoelectricity. Concurrent work in

progress has also shown that selective ring opening poly-

merization of cyclotrisiloxanes of the type, (RMeSiO) 3, can

give stereoregular polymers under the appropriate conditions.

These results will be communicated in due course.

ACKNOWLEDGEMENTS

The author acknowledges the many contributions to this

work of his co-workers, Mr. Paul S. Epstein, Dr. Larry G.

Bell, and Dr. Wayne A. Gustavson. Financial support from

the Office of Naval Research is gratefully acknowledged.

I i _ _ _ _ _ _ _ _ _ _ _ii I

REFERENCES

1. R.L. Banks, Fortschrit. Chem. Forschung, 25, 71 (1972).

2. T.J. Katz, Adv. Organometal. Chem., 16, 283 (1977).

3. R.H. Grubbs, Pr. Inorg. Chem., 24, 1 (1978).

4. R. Damrauer, Organometal. Chem. Rev. A, 8, 67 (1972).

5. D.R. Weyenberg and L.E. Nelson, J. Org. Chem., 30,

2618 (1965).

6. W.R. Bamford, J.C. Lovie and J.A.C. Watt, J. Chem. Soc.

C, 1137 (1966).

7. C.S. Cundy, C. Eaborn, and M.F. Lappert, J. Organometal.

Chem., 44, 291 (1972).

8. C.S. Cundy, M.F. Lappert, J. Dubac, and P. Mazerolles,

J. Chem. Soc. Dalton, 910 (1976).

9. U. Schubert and A. Rengste, J. Organometal. Chem., 170,

C37 (1979).

10. H. Sakurai and T. Imai, Chem. Lett., 811 (1975).

11. R.F. Hartley and P.N. Vezey, Adv. Organometal. Chem.,

15, 189 (1977).

12.. J. Greene and M.D. Curtis, Inorg. Che ., 17, 2324 (1978).

13. M.D. Curtis and J. Greene, J. :m. Chem. Soc., 100, 6362

(1978).

14. J. Greene and M.D. Curtis, J. Am. Chem. Soc., 99, 5176

(1977).

15. M.D. Curtis, J. Greene, and W.M. Butler, J. Organometal.

Chem., 164, 371 (1979).

16. Retention of configuration at Si has been shown in

metal complex-catalyzed hydrosilation reactions:

L.H. Sommer, K.W. Michael, and H. Fujimoto, J. Am.

Chem. SOC., 89, 1519 (1967).

17. W.A. Gustavson, L.G. Bell and M.D. Curtis, submitted

for publication.

18. W.A. Gustavson, P.S. Epstein, and M.D. Curtis, J.

Organometal. Chem., 000, 000 (1982).

19. 1. Ojima, S.-I. Inaba, T. Kogure, and Y. Nagai, J.

Organometal. Chem., 55, C7 (1973).

20. M.D. Curtis and P.S. Epstein, Adv. Organomet. Chem.,

19, 213 (1981).

21. W.A. Gustavson and M.D. Curtis, to be published.

Table I. Redistribution Products of 1,3-dimethyl-l,3-

diphenyldisiloxane (E' PEP ) a

Product Col. 1bc Col. 2de Col. 3ef

area % area % area %

PhMe2 SiH 4.8 5.9 9.1

Ph2MeSiH 12.2 24.5 75.5

Ph-Ph 0.1 6.5 2.7

MePh2SiSiPhMeH 9.0 339 -

MePh2SiSiPhMe2 5.4 0 . 6 h -

E9E2 P 2.9 5.1 -

EPE1P 10.3 3.6 -

E PEf PP 6.0 0.3 -

EPDPE 'P 7.2 - -

E 'P D PEOP 29.32

a) Only those products which constitute ca. > 5% of thetotal are shown.

b) 0.6 mole % 6 as catalyst in benzene at 60C for 48 hr,77% conversion.

c) Area % of products only, starting material and solventremoved.

d) 4.8 mole % Rh(acac)(C 2H4) catalyst precursor, benzene

solution, 40*C for 1 hr, -20% conversion.

e) The GC column for these runs was not heated high enoughto elute the high boiling polysiloxanes.

f) 0.SM E'PE' P , 1.8mm L2Ir(CO)Cl in benzene at 400C for

38 hr, -60% conversion.

g) Incomplete GC separation from HMePhSiOSiPhMeEt. The Et-group comes from the hydrosilation of the CH 4 in thecatalyst precursor.

2

h) Incomplete GC separation from a trace of EtMePhSiOSiPhMe2.

Table II. Redistribution Products of PhMeSiH 2.

Products Col. aCol. 2 bCol. 3carea % area % area%

Me 2SiH23.

PhMeSiH 2 10.5 - 43.3

PhMe 2SiH 9.8 22.6 8.4

Ph 2SiH 2 14.0 -0.6

Ph 2MeSiH 61.0 58.6 40.1

Ph 3SiH 1.4 18.8 1.2

(HMePhSi) 2 - 6.4

a) 5 mole % lrL 2 (CO)C1 in benzene at 800 for 1 hr.

b) 5 mole % IrL 2 CO)C1 in benzene at BOO for 24 hr.

c) 4 mole % RhL 3C in benzene at 800 for 30 min.

Caption to the Figure

Figure 1. Total ion GC trace of the mixture resulting

from the redistribution reaction of

tetramethyldisiloxane (E'E'), catalyzed by

1% L 3 RhCl (L=Ph 3P) on yf-alumina (calasied at

70 0C for 4 hr in vacuo).

Z0

LU~

Lu

LU

LU

LU u

(vA

w

-~7 LU

~71~ -

ujw

jl

3 Ij omNO;j

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